The present invention is directed toward a cargo handling machines having an elevation mechanism of a parallelogram link type or a jib type for raising and lowering cargoes when driven by an actuator such as an air cylinder or an electric motor.
A previously employed cargo handling machine of this kind uses an air cylinder or an electric motor as a drive source for raising and lowering cargoes. The cargo handling machine using the air cylinder as a drive source adopts either a balance control method or a flow rate control method. The cargo handling machine using the electric motor as a drive source generally adopts either a speed control method or a positioned control method.
However, the aforementioned previously employed control methods provide some inconveniences, which will hereinafter be described. According to the balance control method, a cargo is raised or lowered by constantly supplying the air cylinder with an air pressure corresponding to the weight of the cargo. Since the pressure supplied to the cylinder needs to be set in advance in accordance with the weight of the cargo, it is difficult to consecutively handle various cargoes that differ in weight. Although it is possible to consecutively handle various cargoes that differ in weight using a complex circuit structure and a complex mechanism, this countermeasure causes cost increases in the machine, as well as response deterioration in the machine. In a state where a cargo is suspended in the air, if the air pressure supplied to the cylinder is switched to a value corresponding to a state where no cargo is suspended, the cargo falls almost freely. Consequently, there is a possibility of the cargo or an operator being seriously damaged.
The flow rate control method adjusts a flow rate of air by controlling an opening degree of a flow rate control valve disposed between an air source and a cylinder and thereby makes it possible to raise and lower a cargo. In the course of a transfer from an elevation state to a stationary state, the flow rate control method stops the cargo from moving by closing the flow rate control valve to fix the amount of air in the cylinder. Therefore, an inertia force that serves to raise or lower the cargo is applied to an elevation mechanism immediately after closure of the flow rate control valve. Such an inertia force destroys the balance between the pressure applied to the cylinder and the weight of the cargo. In other words, in transferring from an upward movement to a stationary state, the elevation mechanism keeps moving further upwards due to the inertia force even if the flow rate control valve is closed. As a result, the pressure applied to the cylinder becomes lower than a pressure that is balanced against the weight of the cargo, and the elevation mechanism descends due to the elimination of the inertia force. Accompanied by a repetition of such a process, the bound phenomenon is attenuated and the cargo is finally stopped. Since the flow rate control method invariably causes the aforementioned bound phenomenon, it is inevitable to sacrifice the operability to a certain extent.
Furthermore, the balance control method and the flow rate control method stop the elevation mechanism if a neutral state is achieved in response to cancellation of instructions. The instructions to raise and lower the cargo are based on a neutral point which is indispensable in these methods. The neutral point constitutes an insensitive range. As a result, the cargo may move at an unexpectedly high speed due to excessive input of an instruction signal resulting from a delay in responding to an instruction due to the insensitive range. Should the cargo fall to the floor, there is a possibility of the elevation mechanism arms leaping up high into the air. Although a damper may be used to inhibit the arms from leaping up, the operations of raising and lowering the cargo are adversely affected due to the addition of the operational force of the damper.
The speed control method and the positional control method make it possible to raise and lower cargoes by driving the electric motor based on a speed instruction signal and a positional instruction signal respectively. The cargo is raised or lowered at a speed corresponding to an instruction signal regardless of the weight of the cargo. Since the operator is unable to detect the weight of the cargo, the aforementioned methods are disadvantageous in terms of security. For example, when an instruction is issued to raise a cargo suspended in the air, the operator may not refrain from canceling the instruction even if the cargo interferes with peripheral equipments. This is because the operator cannot detect the increased resistance to the raising of the cargo. As a result, an excessively great external force is applied to the cargo and there is a possibility of the cargo falling to the floor and being damaged.
Still further, as is the case with the aforementioned flow rate control method, the speed control method and the positional control method stop the elevation mechanism if a neutral state is achieved in response to cancellation of instructions. The instructions to raise and lower the cargo are based on a neutral point which is also indispensable in these methods. The neutral point constitutes an insensitive range in raising or lowering the cargo. Therefore, the operation of raising or lowering the cargo invariably starts from the insensitive range. As a result, the cargo may move at an unexpectedly high speed due to excessive input of an instruction signal resulting from a delay in responding to an instruction.
In order to eliminate one or more of the aforementioned inconveniences, the present invention provides a cargo handling machine utilizing a force control method and including an elevation mechanism for raising and lowering a cargo, a drive source for driving the elevation mechanism, a control section having an electropneumatic proportional valve for controlling the drive source and an operating section having a force sensor, wherein the force sensor detects an anti-gravitational lift force generated by a user holding the operating section. A hoisting force of the cargo handling machine is amplified in accordance with the lift force and the cargo is raised or lowered by the lift force and the hoisting force.
In accordance with one aspect of the invention, a cargo handling machine includes an elevation mechanism to raise and lower cargo, a drive source for driving the elevation mechanism to raise and lower a cargo, an operating section coupled to the elevation mechanism and having a force sensor arranged to transmit a signal indicative of a vertical force applied to the operating section by a user, a detector coupled to the elevation mechanism to transmit a signal indicative of the vertical direction of movement of the elevation mechanism, and a control section having an electropneumatic proportional valve for controlling the drive source. The control section is configured to operate the cargo handling machine in a first mode wherein the control section causes the drive source to generate a hoisting force that is amplified in accordance with the signal from the force sensor, and a second mode wherein the hoisting force is reduced at an attenuated time rate of change in response to a decrease in the signal from the force sensor and a signal from the detector indicating vertically downward movement of the elevation mechanism.
In one aspect of the invention, a cargo handling machine includes an elevation mechanism to raise and lower a cargo, a force cylinder for driving the elevation mechanism to raise and lower a cargo, an operating section coupled to the elevation mechanism and having a force sensor arranged to transmit a signal indicative of a vertical force applied to the operating section by a user, a detector coupled to the elevation mechanism to transmit a signal indicative of the vertical speed and direction of movement of the elevation mechanism, and a control section having an electropneumatic proportional valve for controlling the force cylinder and a flow rate switching valve. The control section is configured to operate the cargo handling machine in a first mode wherein the control section causes the force cylinder to generate a hoisting force that is amplified in accordance with the signal from the force sensor, and a second mode wherein the control section causes the flow rate switching valve to limit the rate of air supplied to the cylinder so as to limit a speed at which the cargo ascends.
In one aspect, a cargo handling machine includes an elevation mechanism to raise and lower a cargo; a force cylinder for driving the elevation mechanism to raise and lower a cargo; an operating section coupled to the elevation mechanism and having a force sensor arranged to transmit a signal indicative of a vertical force applied to the operating section by a user; and a switch selectively activated by the user; and a control section having an electropneumatic proportional valve for controlling the force cylinder, and a flow rate switching valve. The control section is configured to operate the cargo handling machine in a first mode wherein the control section causes the force cylinder to generate a hoisting force that is amplified in accordance with a signal from the force sensor, and a second mode wherein the control section causes the flow rate switching valve to limit the flow rate supplied to the force cylinder so as to limit the speed at which the cargo ascends or descends.
In one aspect, a cargo handling machine includes an elevation mechanism to raise and lower a cargo, a force cylinder for driving the elevation mechanism to raise and lower a cargo, a force cylinder for driving the elevation mechanism to raise and lower a cargo, an operating section having a force sensor arranged to transit a signal indicative of a vertical force applied to the operating section by a user, an acceleration detector coupling the operating section to the elevation mechanism and transmitting a signal indicative of the vertical acceleration of the operating section, a detector coupled to the elevation mechanism to transmit a signal indicative of the vertical direction of movement of the elevation mechanism, and a control section having an electropneumatic proportional valve for controlling the force cylinder, a pressure regulating valve for supplying a preselected fluid pressure, and an electromagnetic valve for selectively introducing the preselected pressure from the pressure regulating valve to an upper chamber of the force cylinder. The control section is configured to operate the cargo handling machine in a first mode wherein the control section causes the drive source to generate a hoisting force that is amplified in accordance with a signal from the force sensor, and a second mode wherein the control section causes the electromagnetic valve to introduce the preselected pressure to the upper chamber of the force cylinder in response to a rate of change in the signal from the force sensor that exceeds a preselected value, a signal from the acceleration detector indicating a vertically upward acceleration of the operating section, and a signal from the detector indicating vertically upward movement of the elevation mechanism.